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Jan. 22, 1963
A. TURKEVICH
3,074,863
METHOD OF OPERATING A NEUTRONIC REACTOR
Filed May 12, 1945
2 Sheets-Sheet 1
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Jan. 22, 1963
A. TURKEVICH
3,074,863
METHOD OF OPERATING A NEUTRONIC REACTOR
Filed May 12, 1945
2 Sheets-Sheet 2
FIE-Z.
cc
3&745858
Patented Jan. 22, 1953
2
3,874,868
METHQD 0F GPERATING A NEUTRGNIC
REACTQR
Anthony Turlrevicb, Chicago, Ill, assignor to the United
States oi’ America as represented by the United States
Atomic Energy {Zommission
Fiied May 12, 1945, Ser. No. 593,509
1 ‘Claim. (Ci. 204-4543)
suspension including a slurry of natural uranium oxide
or carbide in- D20 or a solution or slurry of a uranium
compound, such as, uranyl sulphate, uranyl nitrate, U02
etc. containing more than natural concentrations of U285
in ordinary Water or D20.
Ina reactor of the above described type operating con
tinuously at high‘ neutron densities, radioactive elements
of extremely high capture cross-section may be formed
as, intermediate elements in the decay chains of the ?s~
This invention relates to the general subject of nu
10 sion fragments, thereby causing signi?cant ?uctuations
clear ?ssion, and more particularly to a novel method
inthe reproduction ratio of the reactor. One of the most
and means for bombardment of ?ssionable materials.
important of these decay chains is believed to be the 135
It is known that certain materials such as U233, U235 or
?ssion chain starting with To (short)—>l (6.7 hr.)->Xe
or thermal neutrons, ?ssion or split to yield fragments 15 (9.2 hr.)—> Cs (long lived)-*Ba (stable), the parenthetical
times indicating half-lives. The neutron absorption of
of lower atomic number. These fragments which have
tellurium, iodine, caesium, and barium is relatively un
atomic numbers ranging from about 77 to about 158,
important; however, the neutron capture cross-section of
and, since they are radioactive, the fragments decay into
radioactive xenon has been measured to about
other materials, generally by emission of beta particles.
The fragments and the decay products are known as ?s 20
3,590,000X 10-24
sion products, a majority of which comprise a light group
cm?, many times larger than that of stable gadolniurn,
94239, when subjected to neutron bombardment by slow
of atomic numbers about 35 to 46 and a heavy group
of atomic numbers about 51 to 60.
for example, the cross-section of which is 3O,000><10—24
cm.2. Upon adsorption of a neutron, xenon135 shifts to
an element of relatively small capture cross
tice has required interruption of the bombardment for 25 xenonm,
section. The above mentioned’ ?uctuations in the repro
treatment of the ?ssionable composition to remove the
duction ratio of the reactor correspond in period to the
?ssion products and other products of the reaction (in
appearance and decay of xenon135.
cluding element 94-). Removal of ?ssion products is
The rate of production of the initiating fragment is
generally regarded as important because of the objection
a function of the neutron density to which the uranium
able radioactivity acquired by the mass undergoing bom 30 containing material is exposed, and is, therefore, de
bardment and also because certain of the ?ssion prod
pendent upon the power at which the reactor is operat
ucts, particularly a xenon isotope, has an objectionablyv
ing. The radioactive xenon135 is produced with a no
After substantial bombardment has occurred usual prac
high neutron absorption cross-section.
ticeable effect on the reaction a few hours after the reac
A particularly e?ective method of establishing neutron
tion is started, and this c?ect becomes greater as the
bombardment as herein contemplated involves the estab 35 neutron
density is increased and maintained.
lishment of a self-sustaining neutron chain reaction in a
When the chain reaction has been initiated and the
neutronic reactor. in neutronic reactors a neutron ?ssion
neutron density within the reactor has been stabilized
able isotope such as U233, U235 or 94239 or mixtures thereof
at a predetermined value by the use of neutron absorbis subjected to ?ssion by absorption of neutrons and a
out control rods, or by varying the volume of slurry or
self-sustaining chain reaction is established by the neu
other suspension within the reactor tank, or by any other
trons evolved by the ?ssion. In general such reactors
desired means, the neutron density drops due to the
comprise bodies of compositions containing such ?ssion
formation of more and more radioactive iodine which
able material, for example, natural uranium, disposed
Llecaysinto xenon135. When Xenon135 is formed in suf
in a neutron slowing material which slow the neutrons
?cient quantities to reduce the reproduction ratio below
to thermal energies. Such a slowing material is termed 45 unity by absorption of neutrons, the neutrons reaction
a neutron moderator. Carbon, beryllium, and D20 are
stops if no compensation is made for this condition.
typical moderators suitable for such use. Speci?c de
tails of the theory and essential characteristics of such
reactors are set forth in co-pending application of Enrico
According to the present invention, however, this prob
lem has been solved by continuously sweeping such poi
soning gases, as xenonm, from the slurry, or other sus
Fermi and Leo Szilard, Serial No. 568,904, ?led Decem 50 pensions thereby minimizing the eilect of this diiiiculty.
ber 19, 1%4, now Patent No. 2,708,656, issued May 17,
Accomplishment of the foregoing constitute some of the
1955.
principal objects, features and advantages of the inven
The removal of ?ssion products from neutron chain re
tion, others of which will become apparent when con
acting compositions in such reactors is particularly desir
sidered in view or" the following description and the
able since the absorption of neutrons by ?ssion products 55 accompanying drawings wherein:
such as Xcnon135 becomes very substantial within a few
FIG. 1 is a diagram illustrating a suitable embodiment
hours and substantially limits the rate at which the re
of the invention, the reactor tank being greatly reduced
action may proceed.
in size; and
in accordance with the present invention it has been
PEG. 2 is a diagram illustrating a modi?cation of the
found that ?ssion products may be removed to a sub 60 invention.
stantial degree from a ?ssionable composition during
Referring to FIG. 1 a neutronic reactor is diagram
neutron bombardment. This may be accomplished by
matically illustrated‘ at 2. Inlet pipe 4 of the reactor is
subjecting to bombardment a liquid ?ssionable material
connected to the discharge side of pump 6, the suction side
moderator composition and removing valuable ?ssion
of which is connected to a heat exchange and puri?cation
products from the composition.
tank 8 which in turn is connected to the outlet pipe 10'
Thus a neutron chain reaction may be established in
a suspension of a ?ssionable isotope in a liquid moderator
of‘ the reactor tank 2.
The suspension which is indicated at 12 is circulated
through the tanks 2 and 8 by the pump ‘6, and is cooled
Within the tank 8 by a coil 14 through which cooling ?uid,
su pension may be removed from the reaction zone treated 70 such as ordinary water, is circulated by any conventional
and the ?ssion products produced swept out by bubbling
gas through the reacting liquid suspension or the liquid
tov remove gaseous ?ssion products and returned to the
reaction zone.
The process may be applied to any liquid
neans such as a pump (not shown).
Poisoning or neutron absorbent gases in the slurry
ace/gees
3
within the heat exchange tank 8 are swept therefrom by
a gas, such as helium, having a low danger coef?cient,
the helium being pumped through an inlet pipe 16 having
a flow meter generally designated 18 consisting of a
mercury ?lled manometer tube 20, the spaced arms 22, 22
'
4i
line 93 communicating with the tank 52 or into line 109
communicating with reservoir 192 into which additional
uranium-containing material may be introduced through
the supply line
The suspension is pumped through
the reservoir ltlZ and the reactor tank ‘52 by a reversible
delivery pump 1%.
of which are connected to the pipe 16 with a restriction
By means of the apparatus above described, the volume
valve 24 disposed intermediate the junction of the re
of suspension as well as the concentration of uranium
spective arms 22', 22 with the pipe 16. By observation
containing materials withinvthe slurry may be controlled.
of the mercury within a manometer tube which is pref
An emergency dump line 168 is also provided, said
erably constructed of glass, the pressure and hence the 10
line communicating with the reservoir 1W2 and through
flow rate of the helium in the pipe 16 may be determined.
a dump valve illil with the reactor tank 52. The valve
As the helium or other gas enters the heat exchange
tank 8, it passes through a screen or baflie 26 which dif
fuses the helium into small bubbles before it passes
through the suspension. The helium and the poisoning
, lib may be opened under emergency conditions to permit
rapid flow of the slurry from the reactor tank to the
reservoir 1532, thereby reducing the body of slurry within
the reactor tank below the critical size at which a chain
reaction may be sustained.
The invention is capable of numerous variations. For
example, gases other than helium such as deuterium, as
containing any suitable material, such as glass Wool 34,
which collects the decay products of the short-lived gas 20 well as nitrogen, methane, argon, xenon other than
xenon135, or similar gas may be used in lieu of helium.
eous ?ssion products. The helium and the long-lived
Moreover, the fissionable suspension may be sprayed into
gaseous ?ssion products then pass through a sulfuric acid
a gas space in a column and collected at the bottom
drying cell 36 into a charcoal trap 33 wherein the long
thereof to remove gaseous ?ssion products as herein con
lived gaseous ?ssion products are absorbed by the char
coal and decay there. The helium then passes from the 25 templated. Alternatively the liquid may be allowed to
flow over a surface in a thin ?lm preferably while passing
trap 33 through the outlet pipe 46) to a suitable reservoir
another gas over the ?lm in order to strip the gases from
(not shown). Thus, the gaseous ?ssion products within
gaseous ?ssion products which are swept from the suspen
sion collectat the top of the tank 8 and pass through a
spray trap 28 into a trap 39 comprising a lead sheath 32
he liquid. Furthermore, in neutronic reactors utilizing
a liquid reactive composition and operated at high power
nomena due to the presence in the slurry of gaseous ?ssion 30 utputs, the liquid moderator, such as water, light or
heavy, dissociates or decomposes under the influence of
products such as xenon135 having relatively greater neutron
the various radiations and ?ssion fragment bombardment.
capture cross-sections.
the slurry are continuously swept therefrom, thereby sub
stantially decreasing the above mentioned poisoning phe
These dissociation gases, in being released from the reac
‘ The decay products may be recovered, if desired, from
tive composition, can be su?icient to carry with them all
traps 3t} and 38 by conventional processes.
35 or part of the neutron absorbent gases and perform the
‘ Referring now to FIG. 2, a modi?cation of the inven—
function of stripping the unwanted gases from the liquid.
tion is illustrated wherein the reactor tank or chamber 52
Thus deliberate introduction of helium or the like can be
contains a body of ?ssionable suspension 54 which is
eliminated or greatly reduced.
.
circulated through a heat exchanger 56 by a pump 58.
Natural uranium compounds, or compounds contain
About 6 metric tons of uranium oxide (U02) and 30
ing U233 or 947-39 in lieu of U235 or enriched compositions
to 40 metric tons of D20 is required to establish a neutron
containing more than natural concentrations of these iso
reaction in such a tank. Cooling fluid, such as water, is
topes may be used as herein contemplated. These com
circulated through the heat exchanger by means of inlet
positions may be suspended or dissolved in the liquid
and outlet pipes 60 and '62, respectively.
moderator.
y
'
A screen or ba?le is provided within the reactor tank
It is also to be noted that while the invention has been
in the form of an aluminum plate 64 with a plurality of
described for use in removing neutron absorbent gases
ports 65, 65 therethrough, and helium gas under pres
from the reacting composition, the means and method
sure is admitted to the bottom 66 of the reactor, through
an inlet line 653 having a control valve 70 therein. The
described and claimed herein are also useful for remov
helium is forced under pressure through the valve '70, 50 ing all ‘gaseous phases of the many decay chains initiated
in the ?ssion fragments. Removal of the radioactive
and passes through the ports 65, 65 in the screen which
material while in a gaseous phase greatly reduces the over
thus diffuses the helium into ?ne bubbles. The bubbles
all radioactivity of the composition and facilitates han
are distributed substantially homogeneously through the
dling thereof at all times. It will be understood that sub
stantially 100 percent of all gaseous substances, for ex‘
ample, xenon and krypton are swept from the reacting
the helium are conducted from the top of the reactor tank
composition. Thus all the gaseous radioactive elements
52 by an outlet line '72 which passes through a trap ‘74,
are withdrawn from the reactor thereby reducing the over
said trap having conventional means therein for absorb
all radioactivity of the reacting composition. For ex
ing the gaseous ?ssion products and collecting their decay
products. The outlet line '72 may, if desired, be connected 60 ample, the following table lists the percentages of var
ious activities which in their gaseous phases have been
to any convenient means such as a pump (not shown) for
experimentally swept from the reacting composition in
evacuating the helium from the top of the reactor tank 52.
accordance with the above described process.
Small quantities of the suspension are continuously
withdrawn from the tank 52 through an outlet pipe 78
Activity identi?ed
Percent
which conveys the slurry to a device 86 for separating 65
swept out
the moderator ?uid from the uranium-containing solids.
The uranium-containing solids are withdrawn from the
slurry and pass upwardly therethrough sweeping gaseous
?ssion products therefrom; and these products along with
device 80 through the pipe 82. whereupon the elements
93, 94 and the ?ssion products may be separated from one
another. The moderator ?uid is pumped from the device 70
Si) by a pump 84 through a pipe 86 to a puri?cation tank
83 from which the moderator fluid passes to a supply
tank 9i) which is also connected by line 92 to a supply
Ba (12.5 days) + La (40 hrs.)
20. 6
Sr (55 days) __________ __
97. 5
Sr (30 years) + Y (60 h
3.4
Ge (28 days) _________ __
c
Ge (3/20 days) -I— Pr (17 min.) _____ __
c
Zr (65 days) _____________________ __
_
Y (57 days) ________________________________________________ _.
0. 38
.0125
.073
13. 3
Although the present invention has been described with
source (not shown). The moderator ?uid is urged by
particular
reference to the speci?c details of certain em
75
pump 94 through a three-way valve 96 either into the
5
3,074,868
6
bodiments thereof it is not intended that such details
shall be regarded as limitations upon the scope of the
invention except insofar as included in the accompanying
claim.
What is claimed is:
In the method of operating a self-sustaining neutronic
reactor comprising subjecting to neutron bombardment
a ?uid composition consisting of a suspension of approxi~
mately six metric tons of uranium oxide in thirty to
forty metric tons of D20, the step of continuously pass 10
‘,ing ‘deuterium through the ?uid composition thereby
sweeping from the ?uid composition gaseous ?ssion prod
ucts resulting from the nuclear reaction and separating
the deuterium from said gaseous ?ssion products.
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,725,925
1,749,561
Kent ________________ __ Aug. 27, 1929
Cadman ______________ __ Mar. 4, 1930
1,756,018
1,916,922
2,050,025
2,708,656
Dubbs ______________ __ Apr. 29,
Dow ________________ __ July 4,
Sullivan et a1 ___________ __ Aug. 4,
Fermi et al. __________ __ May 17,
1930
‘1933
1936
1955
FOREIGN PATENTS
314,427
114,150
1114,1521
Great Britain __________ ___ Dec. 1, 1930
Australia _____________ __ May 2, 1940
Australia _____________ __ May 3, 1940
861,390
233,011
France ______________ __ Oct. 28, 1940
Switzerland ____________ ___ Oct. 2, 1944
OTHER REFERENCES
A.E.C.D.—306v3 US. Atomic Energy Comm, Water
15 Boiler, September 4, 1944, pp. 142. Available from
A.E.C. Technical Information Service, Oak Ridge, Tenn.
Kelly et al.: Physical Review 73, 1135-9‘ (1948).
Copy in Patent O?‘ice Library.
.